MongoDB $elemMatch

Summary: in this tutorial, you’ll learn how to use the MongoDB $elemMatch operator to select documents from a collection.

Introduction to the MongoDB $elemMatch operator

The $elemMatch is an array query operator that matches documents that contain an array field and the array field has at least one element that satisfies all the specified queries.

The $elemMatch has the following syntax:

{ <arrayField>: {$elemMatch: { <query1>, <query2>, ...} } }
Code language: HTML, XML (xml)

In this syntax:

• First, specify the name of the array field.
• Second, specify a list of queries that you want at least one element in the <arrayField> to meet the query criteria.

Notice that you cannot specify a $where expression or a $text query expression in an $elemMatch.

MongoDB $elemMatch operator examples

We’ll use the following products collection for the demonstration:

db.products.insertMany([
	{ "_id" : 1, "name" : "xPhone", "price" : 799, "releaseDate" : ISODate("2011-05-14T00:00:00Z"), "spec" : { "ram" : 4, "screen" : 6.5, "cpu" : 2.66 }, "color" : [ "white", "black" ], "storage" : [ 64, 128, 256 ] },
	{ "_id" : 2, "name" : "xTablet", "price" : 899, "releaseDate" : ISODate("2011-09-01T00:00:00Z"), "spec" : { "ram" : 16, "screen" : 9.5, "cpu" : 3.66 }, "color" : [ "white", "black", "purple" ], "storage" : [ 128, 256, 512 ] },
	{ "_id" : 3, "name" : "SmartTablet", "price" : 899, "releaseDate" : ISODate("2015-01-14T00:00:00Z"), "spec" : { "ram" : 12, "screen" : 9.7, "cpu" : 3.66 }, "color" : [ "blue" ], "storage" : [ 16, 64, 128 ] },
	{ "_id" : 4, "name" : "SmartPad", "price" : 699, "releaseDate" : ISODate("2020-05-14T00:00:00Z"), "spec" : { "ram" : 8, "screen" : 9.7, "cpu" : 1.66 }, "color" : [ "white", "orange", "gold", "gray" ], "storage" : [ 128, 256, 1024 ] },
	{ "_id" : 5, "name" : "SmartPhone", "price" : 599, "releaseDate" : ISODate("2022-09-14T00:00:00Z"), "spec" : { "ram" : 4, "screen" : 9.7, "cpu" : 1.66 }, "color" : [ "white", "orange", "gold", "gray" ], "storage" : [ 128, 256 ] }
])
Code language: JavaScript (javascript)

1) Using the MongDB $elemMatch opeator example

The following example uses the $elemMatch operator to query documents from the products collection:

db.products.find({
    storage: {
        $elemMatch: {
            $lt: 128
        }
    }
}, {
    name: 1,
    storage: 1
});
Code language: CSS (css)

It matches the documents where the storage is an array that contains at least one element less than 128:

[
  { _id: 1, name: 'xPhone', storage: [ 64, 128, 256 ] },
  { _id: 3, name: 'SmartTablet', storage: [ 16, 64, 128 ] }
]
Code language: JavaScript (javascript)

Summary

• Use the $elemMatch operator to select documents that have an array field. And the array field has at least one element that satisfies specified query criteria.